Geotail and LFM comparisons of plasma sheet climatology: 2. Flow variability

We characterize the variability of central plasma sheet bulk flows with a 6-year Geotail data set and a 2-month Lyon-Fedder-Mobarry (LFM) global MHD simulation at two spatial resolutions. Comparing long databases of observed and simulated parameters enable rigorous statistical tests of the model's ability to predict plasma sheet properties during routine driving conditions and represent a new method of global MHD validation. In this study, we use probability density functions (PDFs) to compare the statistics of plasma sheet velocities in the Geotail observations with those in the LFM simulations. We find that the low-resolution model grossly underestimates the occurrence of fast earthward and tailward flows. Increasing the simulation resolution inherently changes plasma sheet mass transport in the model, allowing the development of fast, bursty flows. These flows fill out the wings of the velocity distribution and bring the PDF into closer agreement with observations.